Arc lamps, such as HMI (Hydrargyrum Medium arc Iodie), Xenon, and mercury arc lamps, require a high voltage discharge to ionize, and sometimes vaporize, the illuminating medium inside the discharge tube.
Traditionally, this arc-starting power has been provided by a very straightforward, if not optimum, circuit comprised of two ganged transformers, the primary of the second transformer (and the secondary of the first transformer) being in series with a spark gap which alternately makes and breaks the circuit as the voltage level rises and falls to create current spikes that cause high voltage in the secondary of the second transformer, which is directly connected to the electrodes inside the arc lamp.
Obviously this system is functional in that it does ignite the arc lamps. It is one of the first systems that an engineer charged with creating an ignitor would conceive of, and has probably been used in the same substantially unchanged form for decades. Very likely the circuit has been used continuously without substantial modification since well before the advent of solid state devices.
As solid state electronics engineering has progressed in sophistication, a circuit which might have been close to optimal according to yesterday's technology becomes subject to improvement by incorporation of the technology of today.
Specifically, although the original ignitor does indeed work, when viewed from the perspective of solid state technology and integrated circuit thinking, it is a heavy-handed approach to the problem and is somewhat inefficient in its operation by virtue of producing unregulated current which is more than is necessary for the job throughout much of its cycle. It also requires an AC source, and materials, such as the transformers, that are three times the weight and twice the size of a more sophisticated unit optimizing the characteristics of weight, size, and efficiency by the use of state-of-the-art electronics.